Alan Rickman inhabited several now-classic roles over the course of his 30-year career, from Hans Gruber to Alexander Dane. But his younger fans in particular probably best knew him as Severus Snape, the surly Hogwarts professor who turns out to have hidden depths. Since Rickman’s death last week, his fans, friends, and colleagues been sharing their favorite memories of him, and this week J.K. Rowling herself — the woman who invented Severus Snape — revealed the “secret” detail she slipped to Rickman to help inform his performance.

Rickman has said in interviews that Rowling let him in on a “tiny, little, left-of-field piece of information” to help him better understand the character. In the wake of his passing, Rowling has finally revealed just what that little tidbit was.

At the time that Rickman was preparing for the first film, Rowling had only completed the first few books in the series, and Snape still appeared to be a loathsome antagonist. However, Rickman revealed to HitFix in 2011, “She gave me one tiny, little, left-of-field piece of information that helped me think that he was more complicated and that the story was not going to be as straight down the line as everybody thought.”

While Rowling wouldn’t give up all the details to Rickman, “[i]t was important for her that I know something, but she only gave me a tiny piece of information which helped me think it was a more ambiguous route,” he said. “What I knew was he was a human being and not an automaton and I knew there was some sense of protection for Harry or I worked that out. It was enough to know, I didn’t know he was a double agent.”

Fans know the word “always” is loaded with meaning for Snape. Near the end of the saga, it’s revealed that Snape has been in love with Harry’s (now deceased) mother Lily since childhood, and has been working as a double agent against Voldemort throughout the entire series. When Dumbledore asks him whether he’s still in love with her “after all this time?” Snape replies, “Always.”

The reveal changed everything Harry Potter fans, and Harry Potter himself, thought they knew about Snape. Rickman does out-and-out villains perfectly well — just look at Hans Gruber in Die Hard — but Rowling’s inside intel was the magic ingredient that helped him turn Snape from a sneering baddie to one of the franchise’s most complicated and beloved heroes.